Standard Rack and EIA-310

What is 19” Rack (Standard Rack)

Organize and Secure Servers and Network Equipment



  • What is EIA-310
  • What is 19” Rack (Standard Rack)
  • Rack Mounting Depth



What is EIA-310

Server rack measurements have been standardized to help unify the design and manufacturing of most server and networking equipment that are designed to be rack-mounted.

EIA-310 is a specification for what is often called the “standard rack”. This specification standardizes several important features of 19” racks, such as the Rack Unit (RU or U), vertical hole spacing, horizontal hole spacing, rack opening and front panel width. The specification also sets tolerances on each of these dimensions. EIA stands for the Electronic Industries Association. The current revision is EIA-310-D.


Rack Unit (U or RU) Space

Server racks are often designated by height, measured in “rack unit” and often abbreviated as U or RU. A rack unit measures 1.75 inches (44.45 mm). Server racks can range from 1U types, typical of small home or office wall-mount racks, to large 48U enclosures intended for high-density data center operations.



Vertical Spacing and U Space

Vertical hole spacing is defined as a repeating pattern of holes within one Rack Unit of 1.75”. The hole spacing alternated at: 1/2” – 5/8” – 5/8” and repeats. The start and stop of the “U” space is in the middle of the 1/2" spaced holes. See the diagram below. The three hole group spacing is measured from center hole to center hole and does not vary, regardless of whether the server rack has square or round mounting holes.

Horizontal Spacing and Rack Opening

The horizontal spacing of the vertical rows of holes is specified at 18 5/16″ or 18.312” (465.1 mm). This dimension is not well maintained on some racks, causing problems with equipment installation. The spacing is measured from center hole to center hole, regardless of whether the server rack has square or round mounting holes.

The opening in the rack is specified as a minimum of 17.72″ (450mm). 2-Post or relay racks tend to have a larger than normal opening, as do many other racks with threaded holes.

Front Panel Width

The term 19″ rack specifies the width of the front panel of equipment. It is also called mounting flange dimension.


Rack Mounting Depth

Rack mount depth is commonly confused with the overall rack depth including the door. The rack mounting depth is defined as the dimension from the front of the front mounting post to the back of the back mounting post. Since many cabinets have adjustable mounting posts, the depth can only be accurately determined by measuring it.

Measuring 4Post Rack Mount Depth

Measuring 2Post Rack Mount Depth (Upright Depth)

2 Post relay rack’s mounting depth is also called the Upright Depth. Relay racks only have two uprights to support the equipment instead of the four uprights that other rackmount cabinets have. The most common upright depth is 3″, although 5″ and 6″ are also readily available.

Relay racks are most commonly used in data closets and back offices where only one or two racks are needed. Servers can be installed in a center mount or flush mount by using rackmount installation kits or shelves.

Purchase guideServer cabinetStandard rack